OBJECTIVES: 1. To develop a technique for determining molecular ultrastructure in the 2-10 Angstrom units range by sandwiching large molecules of proteins, nucleic acids and polymers between thin epitaxial films of gold: 2. To evaluate the contrast and resolution of epitaxially sandwiched large molecules imaged at high resolution by two-beam electron microscopy. METHODS: 1. Preparation of the thin epitaxial substrate by vacuum evaporation; 2. Deposition of the large molecules from buffered salt solution; 3. Sandwiching of the molecules by vacuum evaporation of a further epitaxial layer; 4. Imaging by high voltage (100 KV.) electron microscopy; 5. Contrast analysis using computer simulation two-beam conditions.